1. Field
The present disclosure relates generally to data networking and in particular to a backhaul radio for connecting remote edge access networks to core networks.
2. Related Art
Data networking traffic has grown at approximately 100% per year for over 20 years and continues to grow at this pace. Only transport over optical fiber has shown the ability to keep pace with this ever-increasing data networking demand for core data networks. While deployment of optical fiber to an edge of the core data network would be advantageous from a network performance perspective, it is often impractical to connect all high bandwidth data networking points with optical fiber at all times. Instead, connections to remote edge access networks from core networks are often achieved with wireless radio, wireless infrared, and/or copper wireline technologies.
Radio, especially in the form of cellular or wireless local area network (WLAN) technologies, is particularly advantageous for supporting mobility of data networking devices. However, cellular base stations or WLAN access points inevitably become very high data bandwidth demand points that require continuous connectivity to an optical fiber core network.
When data aggregation points, such as cellular base station sites, WLAN access points, or other local area network (LAN) gateways, cannot be directly connected to a core optical fiber network, then an alternative connection, using, for example, wireless radio or copper wireline technologies, must be used. Such connections are commonly referred to as “backhaul.”
Many cellular base stations deployed to date have used copper wireline backhaul technologies such as T1, E1, DSL, etc. when optical fiber is not available at a given site. However, the recent generations of HSPA+ and LTE cellular base stations have backhaul requirements of 100 Mb/s or more, especially when multiple sectors and/or multiple mobile network operators per cell site are considered. WLAN access points commonly have similar data backhaul requirements. These backhaul requirements cannot be practically satisfied at ranges of 300 m or more by existing copper wireline technologies. Even if LAN technologies such as Ethernet over multiple dedicated twisted pair wiring or hybrid fiber/coax technologies such as cable modems are considered, it is impractical to backhaul at such data rates at these ranges (or at least without adding intermediate repeater equipment). Moreover, to the extent that such special wiring (i.e., CAT 5/6 or coax) is not presently available at a remote edge access network location; a new high capacity optical fiber is advantageously installed instead of a new copper connection.
Rather than incur the large initial expense and time delay associated with bringing optical fiber to every new location, it has been common to backhaul cell sites, WLAN hotspots, or LAN gateways from offices, campuses, etc. using microwave radios. An exemplary backhaul connection using the microwave radios 132 is shown in FIG. 1. Traditionally, such microwave radios 132 for backhaul have been mounted on high towers 112 (or high rooftops of multi-story buildings) as shown in FIG. 1, such that each microwave radio 132 has an unobstructed line of sight (LOS) 136 to the other. These microwave radios 132 can have data rates of 100 Mb/s or higher at unobstructed LOS ranges of 300 m or longer with latencies of 5 ms or less (to minimize overall network latency).
Traditional microwave backhaul radios 132 operate in a Point-to-point (PTP) configuration using a single “high gain” (typically >30 dBi or even >40 dBi) antenna at each end of the link 136, such as, for example, antennas constructed using a parabolic dish. Such high gain antennas mitigate the effects of unwanted multipath self-interference or unwanted co-channel interference from other radio systems such that high data rates, long range and low latency can be achieved. These high gain antennas however have narrow radiation patterns.
Furthermore, high gain antennas in traditional microwave backhaul radios 132 require very precise, and usually manual, physical alignment of their narrow radiation patterns in order to achieve such high performance results. Such alignment is almost impossible to maintain over extended periods of time unless the two radios have a clear unobstructed line of sight (LOS) between them over the entire range of separation. Furthermore, such precise alignment makes it impractical for any one such microwave backhaul radio to communicate effectively with multiple other radios simultaneously (i.e., a “point-to-multipoint” (PMP) configuration).
In wireless edge access applications, such as cellular or WLAN, advanced protocols, modulation, encoding and spatial processing across multiple radio antennas have enabled increased data rates and ranges for numerous simultaneous users compared to analogous systems deployed 5 or 10 years ago for obstructed LOS propagation environments where multipath and co-channel interference were present. In such systems, “low gain” (usually <6 dBi) antennas are generally used at one or both ends of the radio link both to advantageously exploit multipath signals in the obstructed LOS environment and allow operation in different physical orientations as would be encountered with mobile devices. Although impressive performance results have been achieved for edge access, such results are generally inadequate for emerging backhaul requirements of data rates of 100 Mb/s or higher, ranges of 300 m or longer in obstructed LOS conditions, and latencies of 5 ms or less.
In particular, “street level” deployment of cellular base stations, WLAN access points or LAN gateways (e.g., deployment at street lamps, traffic lights, sides or rooftops of single or low-multiple story buildings) suffers from problems because there are significant obstructions for LOS in urban environments (e.g., tall buildings, or any environments where tall trees or uneven topography are present).
FIG. 1 illustrates edge access using conventional unobstructed LOS PTP microwave radios 132. The scenario depicted in FIG. 1 is common for many 2nd Generation (2G) and 3rd Generation (3G) cellular network deployments using “macrocells”. In FIG. 1, a Cellular Base Transceiver Station (BTS) 104 is shown housed within a small building 108 adjacent to a large tower 112. The cellular antennas 116 that communicate with various cellular subscriber devices 120 are mounted on the towers 112. The PTP microwave radios 132 are mounted on the towers 112 and are connected to the BTSs 104 via an nT1 interface. As shown in FIG. 1 by line 136, the radios 132 require unobstructed LOS.
The BTS on the right 104a has either an nT1 copper interface or an optical fiber interface 124 to connect the BTS 104a to the Base Station Controller (BSC) 128. The BSC 128 either is part of or communicates with the core network of the cellular network operator. The BTS on the left 104b is identical to the BTS on the right 104a in FIG. 1 except that the BTS on the left 104b has no local wireline nT1 (or optical fiber equivalent) so the nT1 interface is instead connected to a conventional PTP microwave radio 132 with unobstructed LOS to the tower on the right 112a. The nT1 interfaces for both BTSs 104a, 104b can then be backhauled to the BSC 128 as shown in FIG. 1.
FIG. 2A is a block diagram of the major subsystems of a conventional PTP microwave radio 200A for the case of Time-Division Duplex (TDD) operation, and FIG. 2B is a block diagram of the major subsystems of a conventional PTP microwave radio 200B for the case of Frequency-Division Duplex (FDD) operation.
As shown in FIG. 2A and FIG. 2B, the conventional PTP microwave radio raditionally uses one or more (i.e. up to “n”) T1 interfaces 204A and 204B (or in Europe, E1 interfaces). These interfaces (204A and 204B) are common in remote access systems such as 2G cellular base stations or enterprise voice and/or data switches or edge routers. The T1 interfaces are typically multiplexed and buffered in a bridge (e.g., the Interface Bridge 208A, 208B) that interfaces with a Media Access Controller (MAC) 212A, 212B.
The MAC 212A, 212B is generally denoted as such in reference to a sub-layer of Layer 2 within the Open Systems Interconnect (OSI) reference model. Major functions performed by the MAC include the framing, scheduling, prioritizing (or “classifying”), encrypting and error checking of data sent from one such radio at FIG. 2A or FIG. 2B to another such radio. The data sent from one radio to another is generally in a “user plane” if it originates at the T1 interface(s) or in the “control plane” if it originates internally such as from the Radio Link Controller (RLC) 248A, 248B shown in FIG. 2A or FIG. 2B.
With reference to FIGS. 2A and 2B, the Modem 216A, 216B typically resides within the “baseband” portion of the Physical (PHY) layer 1 of the OSI reference model. In conventional PTP radios, the baseband PHY, depicted by Modem 216A, 216B, typically implements scrambling, forward error correction encoding, and modulation mapping for a single RF carrier in the transmit path. In receive, the modem typically performs the inverse operations of demodulation mapping, decoding and descrambling. The modulation mapping is conventionally Quadrature Amplitude Modulation (QAM) implemented with In-phase (I) and Quadrature-phase (Q) branches.
The Radio Frequency (RF) 220A, 220B also resides within the PHY layer of the radio. In conventional PTP radios, the RF 220A, 220B typically includes a single transmit chain (Tx) 224A, 224B that includes I and Q digital to analog converters (DACs), a vector modulator, optional upconverters, a programmable gain amplifier, one or more channel filters, and one or more combinations of a local oscillator (LO) and a frequency synthesizer. Similarly, the RF 220A, 220B also typically includes a single receive chain (Rx) 228A, 228B that includes I and Q analog to digital converters (ADCs), one or more combinations of an LO and a frequency synthesizer, one or more channel filters, optional downconverters, a vector demodulator and an automatic gain control (AGC) amplifier. Note that in many cases some of the one or more LO and frequency synthesizer combinations can be shared between the Tx and Rx chains.
As shown in FIGS. 2A and 2B, conventional PTP radios 200A, 200B also include a single power amplifier (PA) 232A, 232B. The PA 232A, 232B boosts the transmit signal to a level appropriate for radiation from the antenna in keeping with relevant regulatory restrictions and instantaneous link conditions. Similarly, such conventional PTP radios 232A, 232B typically also include a single low-noise amplifier (LNA) 236, 336 as shown in FIGS. 2A and 2B. The LNA 236A, 236B boosts the received signal at the antenna while minimizing the effects of noise generated within the entire signal path.
As described above, FIG. 2A illustrates a conventional PTP radio 200A for the case of TDD operation. As shown in FIG. 2A, conventional PTP radios 200A typically connect the antenna 240A to the PA 232A and LNA 236A via a band-select filter 244A and a single-pole, single-throw (SPST) switch 242A.
As described above, FIG. 2B illustrates a conventional PTP radio 200B for the case of FDD operation. As shown in FIG. 2B, in conventional PTP radios 200B, then antenna 240B is typically connected to the PA 232B and LNA 236B via a duplexer filter 244B. The duplexer filter 244B is essentially two band-select filters (tuned respectively to the Tx and Rx bands) connected at a common point.
In the conventional PTP radios shown in FIGS. 2A and 2B, the antenna 240A, 240B is typically of very high gain such as can be achieved by a parabolic dish so that gains of typically >30 dBi (or even sometimes >40 dBi), can be realized. Such an antenna usually has a narrow radiation pattern in both the elevation and azimuth directions. The use of such a highly directive antenna in a conventional PTP radio link with unobstructed LOS propagation conditions ensures that the modem 216A, 216B has insignificant impairments at the receiver (antenna 240A, 240B) due to multipath self-interference and further substantially reduces the likelihood of unwanted co-channel interference due to other nearby radio links.
Although not explicitly shown in FIGS. 2A and 2B, the conventional PTP radio may use a single antenna structure with dual antenna feeds arranged such that the two electromagnetic radiation patterns emanated by such an antenna are nominally orthogonal to each other. An example of this arrangement is a parabolic dish. Such an arrangement is usually called dual-polarized and can be achieved either by orthogonal vertical and horizontal polarizations or orthogonal left-hand circular and right-hand circular polarizations.
When duplicate modem blocks, RF blocks, and PA/LNA/switch blocks are provided in a conventional PTP radio, then connecting each PHY chain to a respective polarization feed of the antenna allows theoretically up to twice the total amount of information to be communicated within a given channel bandwidth to the extent that cross-polarization self-interference can be minimized or cancelled sufficiently. Such a system is said to employ “dual-polarization” signaling. Such systems may be referred to as having two “streams” of information, whereas multiple input multiple output (MIMO) systems utilizing spatial multiplexing may achieve successful communications using even more than two streams in practice.
When an additional circuit (not shown) is added to FIG. 2A that can provide either the RF Tx signal or its anti-phase equivalent to either one or both of the two polarization feeds of such an antenna, then “cross-polarization” signaling can be used to effectively expand the constellation of the modem within any given symbol rate or channel bandwidth. With two polarizations and the choice of RF signal or its anti-phase, then an additional two information bits per symbol can be communicated across the link. Theoretically, this can be extended and expanded to additional phases, representing additional information bits. At the receiver, for example, a circuit (not shown) could detect if the two received polarizations are anti-phase with respect to each other, or not, and then combine appropriately such that the demodulator in the modem block can determine the absolute phase and hence deduce the values of the two additional information bits. Cross-polarization signaling has the advantage over dual-polarization signaling in that it is generally less sensitive to cross-polarization self-interference but for high order constellations such as 64-QAM or 256-QAM, the relative increase in channel efficiency is smaller.
In the conventional PTP radios shown in FIGS. 2A and 2B, substantially all the components are in use at all times when the radio link is operative. However, many of these components have programmable parameters that can be controlled dynamically during link operation to optimize throughout and reliability for a given set of potentially changing operating conditions. The conventional PTP radios of FIGS. 2A and 2B control these link parameters via a Radio Link Controller (RLC) 248A, 248B. The RLC functionality is also often described as a Link Adaptation Layer that is typically implemented as a software routine executed on a microcontroller within the radio that can access the MAC 212A, 212B, Modem 216A, 216B, RF 220A, 220B and/or possibly other components with controllable parameters. The RLC 248A, 248B typically can both vary parameters locally within its radio and communicate with a peer RLC at the other end of the conventional PTP radio link via “control frames” sent by the MAC 212A, 212B with an appropriate identifying field within a MAC Header.
Typical parameters controllable by the RLC 248A, 248B for the Modem 216A, 216B of a conventional PTP radio include encoder type, encoding rate, constellation selection and reference symbol scheduling and proportion of any given PHY Protocol Data Unit (PPDU). Typical parameters controllable by the RLC 248A, 248B for the RF 220A, 220B of a conventional PTP radio include channel frequency, channel bandwidth, and output power level. To the extent that a conventional PTP radio employs two polarization feeds within its single antenna, additional parameters may also be controlled by the RLC 248A, 248B as self-evident from the description above.
In conventional PTP radios, the RLC 248A, 248B decides, usually autonomously, to attempt such parameter changes for the link in response to changing propagation environment characteristics such as, for example, humidity, rain, snow, or co-channel interference. There are several well-known methods for determining that changes in the propagation environment have occurred such as monitoring the receive signal strength indicator (RSSI), the number of or relative rate of FCS failures at the MAC 212A, 212B, and/or the relative value of certain decoder accuracy metrics. When the RLC 248A, 248B determines that parameter changes should be attempted, it is necessary in most cases that any changes at the transmitter end of the link become known to the receiver end of the link in advance of any such changes. For conventional PTP radios, and similarly for many other radios, there are at least two well-known techniques which in practice may not be mutually exclusive. First, the RLC 248A, 248B may direct the PHY, usually in the Modem 216A, 216B relative to FIGS. 2A and 2B, to pre-pend a PHY layer convergence protocol (PLCP) header to a given PPDU that includes one or more (or a fragment thereof) given MPDUs wherein such PLCP header has information fields that notify the receiving end of the link of parameters used at the transmitting end of the link. Second, the RLC 248A, 248B may direct the MAC 212A, 212B to send a control frame, usually to a peer RLC 248A, 248B, including various information fields that denote the link adaptation parameters either to be deployed or to be requested or considered.
The foregoing describes at an overview level the typical structural and operational features of conventional PTP radios which have been deployed in real-world conditions for many radio links where unobstructed (or substantially unobstructed) LOS propagation was possible. The conventional PTP radio on a whole is completely unsuitable for obstructed LOS PTP or PMP operation.
More recently, as briefly mentioned, there has been significant adoption of so called multiple input multiple output (MIMO) techniques, which utilizes spatial multiplexing of multiple information streams between a plurality of transmission antennas to a plurality of receive antennas. The adoption of MIMO has been most beneficial in wireless communication systems for use in environments having significant multipath scattering propagation. One such system is IEEE802.11n for use in home networking Attempts have been made to utilize MIMO and spatial multiplexing in line of sight environments having minimal scattering, which have generally been met with failure, in contrast to the use of cross polarized communications. For example IEEE802.11n based Mesh networked nodes deployed at streetlight elevation in outdoor environments often experience very little benefit from the use of spatial multiplexing due to the lack of a rich multipath propagation environment. Additionally, many of these deployments have limited range between adjacent mesh nodes due to physical obstructions resulting in the attenuation of signal levels.
Radios and systems with MIMO capabilities intended for use in both near line of sight (NLOS) and line of sight (LOS) environments are disclosed in U.S. patent application Ser. No. 13/212,036, now U.S. Pat. No. 8,238,318, and Ser. No. 13/536,927, both of which are incorporated herein by reference, and are referred to herein by the term “Intelligent Backhaul Radio” (IBR).
FIGS. 3A and 3B illustrate exemplary embodiments of the disclosed IBRs. In FIGS. 3A and 3B, the IBRs include interfaces 304A, interface bridge 308A, MAC 312A, modem 324A, channel MUX 328A, RF 332A, which includes Tx1 . . . TxM 336A and Rx1 . . . RxN 340A, IBR Antenna Array 348A (includes multiple antennas 352A), a Radio Link Controller (RLC) 356A and a Radio Resource Controller (RRC) 360A. The IBR may optionally include an “Intelligent Backhaul Management System” (or “IBMS”) agent 370B as shown in FIG. 3B. It will be appreciated that the components and elements of the IBRs may vary from that illustrated in FIGS. 3A and 3B.
Embodiments of such intelligent backhaul radios, as disclosed in the foregoing references, include one or more demodulator cores within modem 324A, wherein each demodulator core demodulates one or more receive symbol streams to produce a respective receive data interface stream; a plurality of receive RF chains 340A within IBR RF 332A to convert from a plurality of receive RF signals from IBR Antenna Array 348A, to a plurality of respective receive chain output signals; a frequency selective receive path channel multiplexer within IBR Channel multiplexer 328A, interposed between the one or more demodulator cores and the plurality of receive RF chains, to produce the one or more receive symbol streams provided to the one or more demodulator cores from the plurality of receive chain output signals; an IBR Antenna Array (348A) including: a plurality of directive gain antenna elements 352A; and one or more selectable RF connections that selectively couple certain of the plurality of directive gain antenna elements to certain of the plurality of receive RF chains, wherein the number of directive gain antenna elements that can be selectively coupled to receive RF chains exceeds the number of receive RF chains that can accept receive RF signals from the one or more selectable RF connections; and a radio resource controller, wherein the radio resource controller sets or causes to be set the specific selective couplings between the certain of the plurality of directive gain antenna elements and the certain of the plurality of receive RF chains.
The intelligent backhaul radio may further include one or more modulator cores within IBR Modem 324A, wherein each modulator core modulates a respective transmit data interface stream to produce one or more transmit symbol streams; a plurality of transmit RF chains 336A within IBR RF 332A, to convert from a plurality of transmit chain input signals to a plurality of respective transmit RF signals; a transmit path channel multiplexer within IBR Channel MUX 328A, interposed between the one or more modulator cores and the plurality of transmit RF chains, to produce the plurality of transmit chain input signals provided to the plurality of transmit RF chains from the one or more transmit symbol streams; and, wherein the IBR Antenna Array 348A further includes a plurality of RF connections to couple at least certain of the plurality of directive gain antenna elements to the plurality of transmit RF chains.
The primary responsibility of the RLC 356A in exemplary intelligent backhaul radios is to set or cause to be set the current transmit “Modulation and Coding Scheme” (or “MCS”) and output power for each active link. For links that carry multiple transmit streams and use multiple transmit chains and/or transmit antennas, the MCS and/or output power may be controlled separately for each transmit stream, chain, or antenna. In certain embodiments, the RLC operates based on feedback from the target receiver for a particular transmit stream, chain and/or antenna within a particular intelligent backhaul radio.
The intelligent backhaul radio may further include an intelligent backhaul management system agent 370B that sets or causes to be set certain policies relevant to the radio resource controller, wherein the intelligent backhaul management system agent exchanges information with other intelligent backhaul management system agents within other intelligent backhaul radios or with one or more intelligent backhaul management system servers.
FIG. 3C illustrates an exemplary embodiment of an IBR Antenna Array 348A. FIG. 3C illustrates an antenna array having Q directive gain antennas 352A (i.e., where the number of antennas is greater than 1). In FIG. 3C, the IBR Antenna Array 348A includes an IBR RF Switch Fabric 312C, RF interconnections 304C, a set of Front-ends 308C and the directive gain antennas 352A. The RF interconnections 304C can be, for example, circuit board traces and/or coaxial cables. The RF interconnections 304C connect the IBR RF Switch Fabric 312C and the set of Front-ends 308C. Each Front-end 308C is associated with an individual directive gain antenna 352A, numbered consecutively from 1 to Q.
FIG. 3D illustrates an exemplary embodiment of the Front-end circuit 308C of the IBR Antenna Array 348A of FIG. 3C for the case of TDD operation, and FIG. 3E illustrates an exemplary embodiment of the Front-end circuit 308C of the IBR Antenna Array 348A of FIG. 3C for the case of FDD operation. The Front-end circuit 308C of FIG. 3E includes a transmit power amplifier PA 304D, a receive low noise amplifier LNA 308D, SPDT switch 312D and band-select filter 316D. The Front-end circuit 308C of FIG. 3E includes a transmit power amplifier PA 304E, receive low noise amplifier LNA 308E, and duplexer filter 312E. These components of the Front-end circuit are substantially conventional components available in different form factors and performance capabilities from multiple commercial vendors.
As shown in FIGS. 3D and 3E, each Front-end 308E also includes an “Enable” input 320D, 320E that causes substantially all active circuitry to power-down. Power-down techniques are well known. Power-down is advantageous for IBRs in which not all of the antennas are utilized at all times. It will be appreciated that alternative embodiments of the IBR Antenna Array may not utilize the “Enable” input 320D, 320E or power-down feature. Furthermore, for embodiments with antenna arrays where some antenna elements are used only for transmit or only for receive, then certain Front-ends (not shown) may include only the transmit or only the receive paths of FIGS. 3D and 3E as appropriate.
FIG. 3F illustrates an alternative embodiment of an IBR Antenna Array 348A and includes a block diagram of an IBR antenna array according to one embodiment of the invention relating to the use of dedicated transmission and reception antennas. In some IBR embodiments the embodiment of FIG. 3C may be replaced with the embodiments described in relation to FIG. 3F. For instance, such substitution may be made in use with either FDD, TDD, or even non-conventional duplexing systems. FIG. 3F illustrates an antenna array having QR+QT directive gain antennas 352A (i.e., where the number of antennas is greater than 1). In FIG. 3F, the IBR Antenna Array 348A includes an IBR RF Switch Fabric 312F, RF interconnections 304C, a set of Front-ends 309F and 310F and the directive gain antennas 352A. The RF interconnections 304C can be, for example, circuit board traces and/or coaxial cables. The RF interconnections 304C connect the IBR RF Switch Fabric 312F and the set of Front-end Transmission Units 309F and the set of Front-end Reception Units 310F. Each Front-end transmission unit 309F is associated with an individual directive gain antenna 352A, numbered consecutively from 1 to QT. Each Front-end reception unit 310F is associated with an individual directive gain antenna 352A, numbered consecutively from 1 to QR. The present embodiment may be used, for example, with the antenna array embodiments of FIG. 3I, 3J, or embodiments described elsewhere. Such dedicated transmission antennas are coupled to front-end transmission units 309F and include antenna element 352A.
In alternative embodiment, the IBR RF Switch fabric 312F may be bypassed for the transmission signals when the number of dedicated transmission antennas and associated front-end transmission units (QT) is equal to the number of RF transmission signals RF-Tx-M (e.g. QT=M), resulting in directly coupling the IBR RF 336A transmissions to respective transmission front-end transmission units 309F. The dedicated reception antennas, including an antenna element 352A in some embodiments, are coupled to front-end reception units 310F, which in the present embodiment are coupled to the IBR RF Switch Fabric. In an additional alternative embodiment, the IBR RF Switch fabric 312F may be bypassed for the reception signals when the number of dedicated reception antennas and associated front-end reception units (QR) is equal to the number of RF reception signals RF-Rx-N (e.g. QR=N), resulting in directly coupling the IBR RF 340A reception ports to respective front-end reception units 310F.
FIG. 3G is a block diagram of a front-end transmission unit according to one embodiment of the invention relating to the use of dedicated transmission and reception antennas, and FIG. 3H is a block diagram of a front-end reception unit according to one embodiment of the invention relating to the use of dedicated transmission and reception antennas. As shown in FIGS. 3G and 3H, each Front-end 309F and 310F also includes a respective “Enable” input 325F, 330F that causes substantially all respective active circuitry to power-down, and any known power-down technique may be used. Power-down is advantageous for IBRs in which not all of the antennas are utilized at all times. It will be appreciated that alternative embodiments of the IBR Antenna Array may not utilize the “Enable” input 325F, 330F or any power-down feature. Furthermore, for some embodiments associated with FIG. 3F for example (with antenna arrays where some antenna elements are used only for transmit or only for receive) then certain Front-ends may include only the transmit 309F or only the receive paths 310F of FIGS. 3G and 3H as appropriate. With respect to FIG. 3G, Bandpass filter 340G receives transmission signal RF-SW-Tx-qt, provides filtering and couples the signal to power amplifier 304G, then to low pass filter 350G. The output of the lowpass filter is then coupled to dedicated transmission antenna, which includes directive antenna element 352A. With respect to FIG. 3H, directive antenna element 352A is a dedicated receive only antenna and coupled to receive filter 370H, when is in turn coupled to LNA 308H. The resulting amplified receive signal is coupled to band bass filter 360H, which provides output RF-SW-Rx-qr.
As described above, each Front-end (FE-q) corresponds to a particular directive gain antenna 352A. Each antenna 352A has a directivity gain Gq. For IBRs intended for fixed location street-level deployment with obstructed LOS between IBRs, whether in PTP or PMP configurations, each directive gain antenna 352A may use only moderate directivity compared to antennas in conventional PTP systems at a comparable RF transmission frequency.
As described in greater detail in U.S. patent application Ser. No. 13/212,036, now U.S. Pat. No. 8,238,318, and Ser. No. 13/536,927 and incorporated herein by reference, various antenna configurations may be utilized in point-to-point and point-to-multipoint embodiments of the current invention. With reference to FIG. 3I, a block diagram of an exemplary IBR antenna array is depicted. Such an array may also be used in part or in entirety as a receive and/or transmit antenna array for an IBR device according to one embodiment of the invention. As the array includes a plurality of antenna panels (310I-A . . . D, 330I, for example), each panel may include one of the antenna structures or individual antennas including the antenna structures. In an IBR device, normally two such antenna arrays including some or all of the antenna panels depicted in FIG. 3I would be utilized with an azimuthal directional bias different for each array or for each collection of one or more such antenna panels to optimize link performance between the instant IBR and the source and destination devices.
While FIG. 3I is a diagram of an exemplary horizontally arranged intelligent backhaul radio antenna array, FIG. 3J is a diagram of an exemplary vertically arranged intelligent backhaul radio antenna array that may also be used in part or in entirety as a receive and/or transmit antenna array for an IBR device according to one embodiment of the invention. The depicted antenna arrays shown in FIGS. 3I and 3J are intended for operation in the 5 to 6 GHz band. Analogous versions of the arrangement shown in FIGS. 3I and 3J are possible for any bands within the range of at least 500 MHz to 100 GHz as will be appreciated by those of skill in the art of antenna design.
The exemplary transmit directive antenna elements depicted in FIGS. 3I and 3J include multiple dipole radiators arranged for either dual slant 45 degree polarization (FIG. 3I) or dual vertical and horizontal polarization (FIG. 3J) with elevation array gain as described in greater detail in U.S. patent application Ser. No. 13/536,927 and incorporated herein. In one exemplary embodiment, each transmit directive antenna element has an azimuthal beam width of approximately 100-120 degrees and an elevation beam width of approximately 15 degrees for a gain Gqt of approximately 12 dB.
The receive directive antenna elements depicted in FIGS. 3I and 3J include multiple patch radiators arranged for either dual slant 45 degree polarization or dual vertical and horizontal polarization with elevation array gain and azimuthal array gain as described in greater detail in U.S. patent application Ser. No. 13/536,927 and incorporated herein. In one exemplary embodiment, each receive directive antenna element has an azimuthal beam width of approximately 40 degrees and an elevation beam width of approximately 15 degrees for a gain Gqr of approximately 16 dB.
Preliminary measurements of exemplary antenna arrays similar to those depicted in FIG. 3I show isolation of approximately 40 to 50 dB between individual transmit directive antenna elements and individual receive directive antenna elements of same polarization with an exemplary circuit board and metallic case behind the radiating elements and a plastic ray dome in front of the radiating elements. Analogous preliminary measurements of exemplary antenna arrays similar to those depicted in FIG. 3J show possible isolation improvements of up to 10 to 20 dB for similar directive gain elements relative to FIG. 3I.
Other directive antenna element types are also known to those of skill in the art of antenna design including certain types described in greater detail in U.S. patent application Ser. No. 13/536,927 and incorporated herein.
In the exemplary IBR Antenna Array 348A illustrated in FIG. 3A through FIG. 3J, the total number of individual antenna elements 352A, Q, is greater than or equal to the larger of the number of RF transmit chains 336A, M, and the number of RF receive chains 340A, N. In some embodiments, some or all of the antennas 352A may be split into pairs of polarization diverse antenna elements realized by either two separate feeds to a nominally single radiating element or by a pair of separate orthogonally oriented radiating elements. Such cross polarization antenna pairs enable either increased channel efficiency or enhanced signal diversity as described for the conventional PTP radio. The cross-polarization antenna pairs as well as any non-polarized antennas are also spatially diverse with respect to each other. Additionally, the individual antenna elements may also be oriented in different directions to provide further channel propagation path diversity.
The foregoing discussion related to intelligent backhaul radios and relate diagrams have include the use of frequency division duplexing (FDD) and time division duplexing (TDD) techniques and architectures. Such architectures, as discussed, include support of both single input and single output (SISO) supporting single stream operation, and multiple input/multiple output (MIMO) multiple stream operation support. Additional embodiments supporting SISO and MIMO technology in specific embodiments include the use so-called zero division duplexed (ZDD) intelligent backhaul radios (ZDD-IBR), as disclosed in U.S. patent application Ser. No. 13/609,156, now U.S. Pat. No. 8,422,540, which is additionally incorporated herein by reference.
Embodiments of the ZDD systems provide for the operation of a IBR wherein the ZDD-IBR transmitter and receiver frequencies are close in frequency to each other so as to make the use of frequency division duplexing, as known in the art, impractical. Arrangements of ZDD operation disclosed in the foregoing referenced application include so-called “co-channel” embodiments wherein the transmit frequency channels in use by a ZDD-IBR, and the receive frequencies are partially or entirely overlapped in the frequency spectrum. Additionally disclosed embodiments of ZDD-IBRs include so-called “co-band” ZDD operation wherein the channels of operation of the ZDD-IBR are not directly overlapped with the ZDD-IBR receive channels of operation, but are close enough to each other so as to limit the performance the system. For example, at specific receiver and transmitter frequency channel separation, the frequency selectivity of the channel selection filters in an IBR transmitter and receiver chains may be insufficient to isolate the receiver(s) from the transmitter signal(s) or associated noise and distortion, resulting in significant de-sensitization of the IBR's receiver(s) performance at specific desired transmit power levels, with out the use of disclosed ZDD techniques. Embodiments of the disclosed ZDD-IBRs include the use of radio frequency, intermediate frequency and base band cancelation of reference transmitter and interference signals from the ZDD-IBR receivers in a MIMO configuration. Such disclosed ZDD techniques utilize the estimation of the channels from the plurality of IBR transmitters to the plurality of IBR receivers of the same intelligent backhaul radio, and the adaptive filtering of the reference signals based upon the channel estimates so as to allow the cancelation the transmitter signals from the receivers utilizing such estimated cancelation signals. Such ZDD techniques allow for increased isolation between the desired receive signals and the ZDD-IBR's transmitters in various embodiments including MIMO (and SISO) configurations.
The support for MIMO operation (FDD, TDD, or ZDD) is highly dependent upon the radio propagation environment between the two radios in communication with each other. The following discussion provides for a general discussion relating to the MIMO channel, and will provide a basis for further discussion. Referring now to FIG. 3K-A the MIMO channel matrix is depicted. Transceiver MIMO Station 3K-05 is in communication with MIMO Station 3K-10 utilizing MIMO channel matrix (Eq. 3K-1) of FIG. 3K-B between the 2 stations of FIG. 3K-A. In an example of a two-by-two MIMO system, two spatial streams are utilized between the two MIMO stations. The channel propagation matrix of Eq. 3K-1 is of order M by N (M rows and N columns). A particular element of the channel propagation matrix, hmn, represents the frequency response of the wireless channel from the nth transmitter to the mth receiver. Therefore each element of the channel propagation matrix H has an individual complex number, if the channel is “frequency flat,” or a complex function of frequency, if the channel is “frequency selective,” which represents the amplitude and phase of the propagation channel between one transmitter and one receiver of MIMO Stations 3K-05 and 3K-10. Often, the channel propagation matrix and the individual propagation coefficients are frequency selective, meaning that the complex value of the coefficients vary as a function of frequency as mentioned. In a rich, multipath scattering environment, as depicted in FIG. 3L, in which sufficient signal strength reaches an intended receiver but is scattered amongst the various structures between a particular MIMO transmitter and MIMO receiver, the spatial distribution of the arriving signals is referred to as a rich multipath environment in which there is a significant angular scattering among the receiving signals at the intended receiver.
In order to separate the MIMO streams received at an intended receiver, such as MIMO Station 3K-05 or MIMO Station 3K-10, the channel propagation matrix H must be determined, as known in the art. The process of determining the channel propagation matrix is often performed utilizing pilot channels, preambles, and/or symbols or other known reference information. Examples of prior art systems utilizing such techniques include IEEE 802.11n, LTE, or HSPA, as well as various embodiments of intelligent backhaul radios per U.S. Pat. Nos. 8,238,818, 8,422,540 and U.S. patent application Ser. No. 13/536,927 as incorporated in their entireties herein.
In order for MIMO systems (including the foregoing mentioned MIMO systems) to support a plurality of spatial MIMO streams, the order of the propagation matrix (referenced as Eq. 3K-1) must equal or exceed the desired number of streams. While this condition is necessary, it is not sufficient. The rank of the matrix must also equal or exceed the number of desired spatial streams. The rank of a matrix is the maximum number of linearly independent column vectors of the propagation matrix. Such terminology is known in the art with respect to linear algebra. The number of supportable MIMO streams must be less than or equal to the rank of the channel propagation matrix. When the propagation coefficients from multiple transmitters of a MIMO station to a plurality of intended receive antennas are correlated, the number of linearly independent column vectors of the channel propagation matrix H is reduced and consequently the system will support fewer MIMO streams. Such a condition often occurs in environments where a small angular spread at the desired intended receiver is present, such as is the case with a line-of-sight environment where the two MIMO stations are a significant distance apart, such that the angular resolution of the receiving antennas at MIMO Station 3K-10 is insufficient to resolve and separate the signals transmitted from the plurality of transmitters at MIMO Station 3K-05. Such a condition is referred to as an ill-conditioned channel matrix for the desired number of streams in the MIMO system, due to the rank of the channel propagation matrix (i.e. the number of linearly independent column vectors) being less than the desired number of MIMO streams between the two MIMO stations. The reasoning behind the rank of the channel propagation matrix being required to be greater than or equal to the desired number of MIMO streams is related to how the individual streams are separated from one another at the intended receiving MIMO station. As is known in the art, the MIMO performance is quite sensitive to the invertability of the channel propagation matrix. Such invertability, as previously mentioned, may be compromised by the receiving antenna correlation, which may be caused by close antenna spacing or small angular spread at the intended MIMO receiver. The line-of-sight condition between two MIMO stations may result in such a small angular spread between the MIMO receivers, resulting in the channel matrix being noninvertible or degenerate. Multipath fading, which often results from large angular spreads amongst individual propagation proponents between two antennas, enriches the condition of the channel propagation matrix, making the individual column vectors linearly independent and allowing the channel propagation matrix to be invertible. The inversion of the channel propagation matrix results in weights (vectors), which are utilized with the desired receive signals to separate the linear combination of transmitted streams into individual orthogonal streams, allowing for proper reception of each individual stream from spatially multiplexed composite information streams. In a line-of-sight environment, all of the column vectors of the channel propagation matrix H may be highly correlated, resulting in a matrix rank of 1 or very close to 1. Such a matrix is noninvertible and ill-conditioned, resulting in the inability to support spatial multiplexing and additional streams (other than by the use of polarization multiplexing, which provides for only 2 streams as discussed).
FIG. 3L illustrates an exemplary deployment of intelligent backhaul radios (IBRs). As shown in FIG. 3L, the IBRs 300L are deployable at street level with obstructions such as trees 303L, hills 308L, buildings 312L, etc. between them. Embodiments of intelligent backhaul radios (IBRs) are discussed in co-pending U.S. patent application Ser. No. 13/212,036, now U.S. Pat. No. 8,238,318, and Ser. No. 13/536,927, the entire contents of which is incorporated herein. The IBRs 300L are also deployable in configurations that include point-to-multipoint (PMP), as shown in FIG. 3L, as well as point-to-point (PTP). In other words, each IBR 300L may communicate with more than one other IBR 300L.
For 3G and especially for 4th Generation (4G), cellular network infrastructure is more commonly deployed using “microcells” or “picocells.” In this cellular network infrastructure, compact base stations (eNodeBs) 316L are situated outdoors at street level. When such eNodeBs 316L are unable to connect locally to optical fiber or a copper wireline of sufficient data bandwidth, then a wireless connection to a fiber “point of presence” (POP) requires obstructed LOS capabilities, as described herein.
For example, as shown in FIG. 3L, the IBRs 300L include an Aggregation End IBR (AE-IBR) and Remote End IBRs (RE-IBRs). The eNodeB 316L of the AE-IBR is typically connected locally to the core network via a fiber POP 320L. The RE-IBRs and their associated eNodeBs 316L are typically not connected to the core network via a wireline connection; instead, the RE-IBRs are wirelessly connected to the core network via the AE-IBR. As shown in FIG. 3L, the wireless connection between the IBRs include obstructions (i.e., there may be an obstructed LOS connection between the RE-IBRs and the AE-IBR). Note that the Tall Building 312L substantially impedes the signal transmitted from RE-IBR 300L to AR-IBR 300L. Additionally, in at least one example scenario, the tree (303L) provides unacceptable signal attenuation between an RE-IBR 300L and the AE-IBR 300L.
As discussed above, the advances in cellular communications, and more specifically the Third Generation Partnership Program's (3GPP, www.3GPP.org) Long Term Evolution (LTE), and associated cellular “off load” use of IEEE 802.11 communication protocols continues to drive the data backhaul requirements of cellular infrastructure sites to ever increasing levels. The need for an increasing number of wireless backhaul links to satisfy the cellular backhaul demand demands the use of potentially congested wireless spectrum resources.
The Federal Communications Commission (FCC) has allowed for the use of currently licensed broadcast television spectrum for use by unlicensed devices. This program has been commonly referred to as the “TV Whitespaces” reuse (http://www.fcc.gov/topic/white-space). A detailed description of the program is provided in FCC order FCC-10-174A1, and the rules for unlicensed devices that operate in the TV bands are set forth in 47 C.F.R. §§15.701-.717. See TITLE 47—Telecommunication; CHAPTER I—FEDERAL COMMUNICATIONS COMMISSION; SUBCHAPTER A—GENERAL, PART 15—RADIO FREQUENCY DEVICES, Subpart H—TELEVISION BAND DEVICES (http://www.ecfr.gov/cgi-bin/text-idx?c=ecfr&SID=30f46f0753577b10de41d650c7adf941&rgn=div6&view=text&node=4 7:1.0.1.1.16.8&idno=47).
The TV Whitespaces program provides for a reuse of underutilized spectrum resources for public use by unlicensed devices (TV Band Devices). Further, so-called “Incumbent Services” remain protected from interference from the TV Band Devices (TVBDs) by a set of operating rules and concepts including (selectively extracted from CFR 47 §15.703 Definitions.):                (a) Available channel. A six-megahertz television channel, which is not being used by an authorized service at or near the same geographic location as the TVBD and is acceptable for use by an unlicensed device under the provisions of this subpart.        (b) Contact verification signal. An encoded signal broadcast by a fixed or Mode II device for reception by Mode I devices to which the fixed or Mode II device has provided a list of available channels for operation. Such signal is for the purpose of establishing that the Mode I device is still within the reception range of the fixed or Mode II device for purposes of validating the list of available channels used by the Mode I device and shall be encoded to ensure that the signal originates from the device that provided the list of available channels. A Mode I device may respond only to a contact verification signal from the fixed or Mode II device that provided the list of available channels on which it operates. A fixed or Mode II device shall provide the information needed by a Mode I device to decode the contact verification signal at the same time it provides the list of available channels.        (c) Fixed device. A TVBD that transmits and/or receives radiocommunication signals at a specified fixed location. A fixed TVBD may select channels for operation itself from a list of available channels provided by a TV bands database, initiate and operate a network by sending enabling signals to one or more fixed TVBDs and/or personal/portable TVBDs. Fixed devices may provide to a Mode I personal/portable device a list of available channels on which the Mode I device may operate under the rules, including available channels above 512 MHz (above TV channel 20) on which the fixed TVBD also may operate and a supplemental list of available channels above 512 MHz (above TV channel 20) that are adjacent to occupied TV channels on which the Mode I device, but not the fixed device, may operate.        (d) Geo-location capability. The capability of a TVBD to determine its geographic coordinates within the level of accuracy specified in §15.711(b)(1), i.e. 50 meters. This capability is used with a TV bands database approved by the FCC to determine the availability of TV channels at a TVBD's location.        (e) Mode I personal/portable device. A personal/portable TVBD that does not use an internal geo-location capability and access to a TV bands database to obtain a list of available channels. A Mode I device must obtain a list of available channels on which it may operate from either a fixed TVBD or Mode II personal/portable TVBD. A Mode I device may not initiate a network of fixed and/or personal/portable TVBDs nor may it provide a list of available channels to another Mode I device for operation by such device.        (f) Mode II personal/portable device. A personal/portable TVBD that uses an internal geo-location capability and access to a TV bands database, either through a direct connection to the Internet or through an indirect connection to the Internet by way of fixed TVBD or another Mode II TVBD, to obtain a list of available channels. A Mode II device may select a channel itself and initiate and operate as part of a network of TVBDs, transmitting to and receiving from one or more fixed TVBDs or personal/portable TVBDs. A Mode II personal/portable device may provide its list of available channels to a Mode I personal/portable device for operation on by the Mode I device.        (g) Network initiation. The process by which a fixed or Mode II TVBD sends control signals to one or more fixed TVBDs or personal/portable TVBDs and allows them to begin communications.        (h) Operating channel. An available channel used by a TVBD for transmission and/or reception.        (i) Personal/portable device. A TVBD that transmits and/or receives radiocommunication signals at unspecified locations that may change. Personal/portable devices may only transmit on available channels in the frequency bands 512-608 MHz (TV channels 21-36) and 614-698 MHz (TV channels 38-5 ).        (j) Receive site. The location where the signal of a full service television station is received for rebroadcast by a television translator or low power TV station, including a Class A TV station, or for distribution by a Multiple Video Program Distributor (MVPD) as defined in 47 U.S.C. 602(13).        (k) Sensing only device. A personal/portable TVBD that uses spectrum sensing to determine a list of available channels. Sensing only devices may transmit on any available channels in the frequency bands 512-608 MHz (TV channels 21-36) and 614-698 MHz (TV channels 38-51).        (l) Spectrum sensing. A process whereby a TVBD monitors a television channel to detect whether the channel is occupied by a radio signal or signals from authorized services.        (m) Television band device (TVBD). Intentional radiators that operate on an unlicensed basis on available channels in the broadcast television frequency bands at 54-60 MHz (TV channel 2), 76-88 MHz (TV channels 5 and 6), 174-216 MHz (TV channels 7-13), 470-608 MHz (TV channels 14-36) and 614-698 MHz (TV channels 38-51).        (n) TV bands database. A database system that maintains records of all authorized services in the TV frequency bands, is capable of determining the available channels as a specific geographic location and provides lists of available channels to TVBDs that have been certified under the Commission's equipment authorization procedures. TV bands databases that provide lists of available channels to TVBDs must receive approval by the Commission.        
Under the white spaces rules, TVBDs (other than TVBDs that rely on spectrum sensing) have the requirement of registering with the TV bands database, and determining available channels of operation. This process requires providing the database the FCC_ID, serial number, geographic location, and other information to the database, to receive a list of available channels for operation. TVBDs are further required to periodically re-register with the database to re-determine available channels of operation. An example of a database entry information for a Fixed TVDB is provided within CFR 47 §15.713 TV bands database (f) Fixed TVBD registration (extraction follows).                (1) Prior to operating for the first time or after changing location, a fixed TVBD must register with the TV bands database by providing the information listed in paragraph (f)(3) of this section.        (2) The party responsible for a fixed TVBD must ensure that the TVBD registration database has the most current, up-to-date information for that device.        (3) The TVBD registration database shall contain the following information for fixed TVBDs:                    (i) FCC identifier (FCC ID) of the device;            (ii) Manufacturer's serial number of the device;            (iii) Device's geographic coordinates (latitude and longitude (NAD 83) accurate to +/−50 m);            (iv) Device's antenna height above ground level (meters);            (v) Name of the individual or business that owns the device;            (vi) Name of a contact person responsible for the device's operation;            (vii) Address for the contact person;            (viii) E-mail address for the contact person;            (ix) Phone number for the contact person.                        
The foregoing is intended to provide a brief overview of the concepts and rules associated with the TV White spaces device operation.
While suitable for use by some wireless applications, such a system is not ideal for use in many highly reliable wireless backhaul applications. As one example, the lack of protection from interference for TVBD registered devices is a significant impediment for achieving a highly reliable data link for backhaul applications in view of interference from unlicensed or other wireless devices, including other TVBD devices. As another example, there is no approach for devices to arbitrate interference amongst one another. There are significant number of other deficiencies of the TV white spaces rules making them non-ideal for use in other bands, and in other applications of use such as cellular backhaul.